Receivers are required to work even when signals are weak. A receiver normally includes a sync detector. During transmission, the sync detector uses a sync word to synchronize a data transmission by indicating the end of header information and the start of data. Normally, the sync detector will calculate a plurality of sync word decision results in response to received sync words. Further, matching of sync word decision results with a pre-stored sync word at the sync detector indicates the received signal quality. Due to a weak signal, there may be only one sync word decision result that matches the pre-stored sync word. Taking 4 frequency-shift keying (4FSK) as an example, a sync word includes 24 symbols. Due to noise, there is a certain randomness for matching a phase with only 24 symbols included in a sync word. Further, in general, the lower a demodulation rate of the receiver, the better to reduce the system power consumption and cost. Therefore, there is at least 1/16 symbol error in the resolution of the phase, due to an oversample rate of 8. Actual simulation shows that such resolution requirements are not enough for particularly high requirement system. On the other hand, increasing the resolution will significantly increase the cost. Therefore, it is desirable to improve accuracy of synchronizing phase for receivers.